Posted
by
kdawsonon Sunday January 18, 2009 @03:25PM
from the geo-exchange dept.

suraj.sun recommends a CNet post giving details of a still little-known energy technology: the ground source heat pump or geo-exchange system. This is distinct from so-called geothermal energy, which taps the heat in the earth to provide energy. Geo-exchange is suitable in scale for small industry — the article describes one commercial re-development of an old mill into apartment and commercial space that put in a geo-exchange at about half the cost of traditional fossil fuel-based alternatives. Even some individual homeowners are opting for this green method of heating and cooling, at a premium in price of about 50 percent (but costs are very much per-project, largely because drilling is involved). "Rather than use underground heat, geothermal heat pumps attached to buildings capitalize on the steady temperature of the ground or deep water wells. In effect, they treat the Earth like a giant energy savings bank, depositing or withdrawing heat depending on the time of year. "

I work in construction and land development in Western Canada, and every single project we work on uses geo-exchange systems, because we get huge tax incentives to utilize energy-efficient technologies (and as strata owners, we still get to charge standard amounts for utilities). This isn't a big city, and there's THREE places that offer geo-exchange services.

This technology has been around for some time, but it fails to generate much PR. You can get a measley $8000 US federal tax credit for installing one. A few enlightened states (not mine) will give you some additional tax credits for installing one.

The expensive part seems to be drilling the earth and laying the hose. However, what they fail to mention is that once its installed, it will last 50+ years.

The parent also mentions open and closed loop, but fail to talk about direct exchange aka DX, which would make more sense for a lot of people.

"The direct exchange (DX) system is a series of copper tubes buried 4 to 6 feet below ground level. Refrigerant gas is then fed through these tubes creating a direct heat exchange between the temperature of the ground and the heat transfer medium, which in this case is the refrigerant gas. Because of this direct exchange feature these systems operate at considerably less operating cost than water source systems and because they do not require the additional water pumping cost and, DX does not suffer the heating or cooling loss associated with transferring the water temperature to the refrigerant as is common with these systems. DX is also cheaper and easier to install as it requires no well drilling or plumbing costs. As copper is a more efficient heat transfer medium than PVC pipe as found in water source, trenching costs are less due to less ground mass being required by DX."

Consider that heat pumps give you on average 3 times more heating or cooling per unit of electricity over resistance heating, for example baseboard heating.

If you ignore the mindless Greenpeace types, and your power is from nukes (like in France) there are no greenhouse gas emissions at all and the air stays nice and clean. Likewise, if you live in the Northwest, where hydro makes a great deal of power and electricity is cheaper and cleaner yet.

One of the big problems with conventional heat pumps is that the coils can ice up in damp cold conditions, like the Northeast USA when temps are 35 degrees F and below. If you ground source, there is no defrost cycle needed, and no noisy fan. You have probably seen a heat pump at some point blow a huge ball of steam off on a cold day at some point, that's the defrost cycle.

When I built my house in 1985, I built a passive solar home (three sided, two-story concrete box with south facing glass and air conduits built into an insulated slab). We placed four solar hot water heaters on the roof as well. The house has repaid the investment many times over, but my one regret is that I allowed myself to be talked out of putting in a geo heat pump system. At the time the experts told me it was too expensive for the projected return. They were wrong of course.

I don't know much about accounting, but it has always seemed to me that carbon cap trading schemes are just a gigantic boondoggle that allow bad actors to continue acting badly. For my money, if governments (Canadian in my case) want to encourage green technology and lower the country's carbon footprint, then they need to very strongly encourage geo heat exchangers in new construction and particularly for green renovations. Solar heating is not always possible, especially this far north, but geothermal exchange is always there.

As a post script, for anyone thinking of installing solar hot water panels on their roof, think again. If it is possible to mount them at ground level on a rack, you achieve two things: A. no holes in your expensive roof, and B. it is much easier to maintain them at ground level.

The Washington Post had an recent article [washingtonpost.com] about this technology being applied in the Washington, DC, area. Slashdot has also featured [slashdot.org] articles [slashdot.org] on similar technologies that use deep water from large lakes or the oceans themselves.

You could remove the need for debris filtering by having a closed loop at the cost of reduced efficiency.

For example you could fill a closed loop with water, and then put one end of the loop (with coils etc) in the lake, and then the other end of the loop either gets welded to the airconditioner coils (to help make the airconditioner more efficient), or is used as you suggest.

Of course you'd still have to clean the end stuck in the lake- stuff is likely to still grow on it.

DX systems suffer because they are burying copper in the ground (which is often aggressive to copper), and then pumping refrigerant through them. any puncture or breach would cause a leak of refrigerant instead of non toxic glycol solution.

DX and "Pump and Dump" geo-exchange systems are both, IMHO, likely to be outlawed in areas with environmental and building codes. Existing systems would probably be grandfathered but in the end I believe closed loop well or "slinky field" type systems will end up the winners.

How does the lifetime compare to PVC though? I've seen PVC that has been buried for 30 years and looks absolutely brand-new (the above-ground portions though - not so much thanks to UV). How does copper compare, since copper corrodes?

My parents built a new house off the beaten path almost 4 years ago, and opted to go with geo-exchange because natural gas isn't available in their area.
The system costs significantly more than a standard one, but heating and cooling costs are HALF of what they were at their old house, which was significantly smaller. According to some back-of-the-napkin numbers my dad crunched, they should hit the break-even point after less than 15 years of use.

About a year ago we installed one of these in our house. The temperature around here varies between -15 C to about +30 C (get with the metric program people) and our heatpump is working wonders with our heating and economy. It cut the costs down to 1/3 of what it used to be and will have paid itself off in less than 5 years with current prices.We drilled about 200m down which gives the best performance for the size of our house.Also we put a large watertank that the heatpump warms up which increases the lifespan of the pump and our next project is to put solar panels that will heat the watertank during mars-oct, thereby increasing the savings even more. It will also "reload" the hole/well that the heatpump takes its heat from increasing the efficiency during winter.Now if I could only produce electricity somehow to power the heatpump (or parts of it) things would be awsome.

I'm amazed that more people don't use this technology. In my opinion there shouldn't be an energy crisis anywhere as all the technology we need to fix things are already availible. More or less anyway.

This technology is fairly well know in the UK and it's getting more popular everyday. The main problem with it is the cost of drilling (apparently it's about double the normal price at the moment because of the Olympic games - everyone that has a drill is down there laying foundations in Londons rubbish soil) as most people don't have enough garden to lay shallow pipe work. Longer term though if a lot of people switched to this technology we would need to upgrade the electricity grid.

<nitpick> In the HVACR industry, "DX" stand for "Direct Expansion", The thing you're referring to needs a different abbreviation. </nitpick>

I know this system has been used, but there can be some problems with it.
Copper piping can have a short life in many soil types.
There will be more refrigerant in the system, which can add some complications and expense.
I wonder how they handle oil return when operating in the heat pump mode?

That would all depend on the size of the heat exchanger, and the duty cycle.

If, for the sake of argument, the typical duty cycle of a functional unit is 50% with say 12sq/ft of surface area on the evaporator, at 45 degrees at the evaporator. If you had 60 degrees at the evaporator, but increased the size to say 24 sq/ft, and the duty cycle to 90%+, it should be no problem. Consider that a system like this would require a pump similar to a swimming pool pump or smaller, which most people that have pools run for 12 hrs/day every day. A system like this wouldn't need to run at 90%+, but it would have that ability.

In reality, it's not even required to run a pump on a system like this. There's a university (I can't remember who off-hand, but a big one) that is currently using a system exactly like this. They don't run pumps, the entire system relies on convection. The cooling itself is free, where the should have huge chillers, lots of freon, and huge power bills. They do still require power to run the fans for circulation inside the buildings, but that's it.

For an ad-hoc system, I made the assumptions of double the size for the "evaporator", and one 1/2hp swimming pool style pond pump, that was able to handle small debris, with a bypass. If convection did it fine, then the pump was a waste. Even still, when I estimated the costs, and I am good at providing complete estimates, it was less than half the price of purchasing a new HVAC.

But, your arguments are valid, and a good example of why people aren't willing to step away from what everyone else has. "Oh, that could never work."

The same could be said of a Peltier/TEC based refrigerator for your car, yet they not only work, but people are very happy with them. Oddly enough, everything I've mentioned is not theory, but working proven fact, that has been implemented. Unfortunately, not widely, because people are afraid to change.

I recall reading about someone in Hawaii doing something like this in order to both generate electricity and clean water by essentially using the deep ocean as the heat sink then the temperature differential to generate electricity (and the condensation for water). Apparently once you got the fluid moving it took less energy to pump it than you could generate with the heat differential in a tropical ocean island.

...I would also point out that Bush's Crawford Ranch [snopes.com] uses a geothermal heat pump.

SHHHHHHHHH! You can't say anything at all good about the president. At least not until after inauguration day!

Seriously, I find it sad that we have an article about geothermal heating and cooling that is used by the private residence of the leader of the free world and it's not mentioned. Seriously, you'd think the article would have brought it up.

Has Bush Derangement Syndrome gotten so bad that saying anything good about Bush is taboo? Or was this a simple, innocent oversight?

It is an odd reversal here, but because sewer rates are so high here and city water metering was the way to measure sewer use. People in the suburbs started drilling wells in my area because it has an easy to get at artesian water table. Without the the use of city water there was no way to tax the sewer use. Got the idea and how it is going to apply?

So the city in it's infinite wisdom decide that wells were 'verboten' no matter what over the whole area. There is no way that you can get a permit.

Now you may think that explaining what you want to do to heat your home would get you a variance. Not simply because the city won't budge, but even more ludicrous is they think you will cheat and not put the water back in the ground as that costs more, but will dump the water into the sewer and increasing the water to the plant for free on your side. Thus making you a thief before found to be one. So easier and cheaper for them is to ban wells period no matter how well intentioned you are to green the planet.

It's to bad I wrote this late as it is not likely to be moderated high enough to get noticed and other point out a similar problem in their area that stops this type of system dead before it lives.

We investigated one here in Finland when we built our house four years ago. They were starting to become very popular about that time since electricity prices just keep going up.

But in any event we were advised not to go that way since the investment would be too large for a house our size (total room area of 130 sq metres).

So we have a air exchange system that heats the incoming air using the outgoing air. It is mandatory in Finland that all new houses have a total air exchange approximately every two hours, so the HVAC system uses the waste heat to both heat the air and any excess heats water (for example extra heat from the bathrooms, sauna or fireplace). The system provides hot water for the underfloor heating as well. That should cut the total power consumption for heating by about 30%.